As a cutting insert which is appropriately used in cutting stainless steel, Patent Document 1 proposes a cutting insert in which a breaker flute is formed so as to form a cross-sectional shape constituted with a land (rake angle θ1), a first inclination face (rake angle θ2), a second inclination face (rake angle θ3) and a steep face, each of which has a positive rake angle, sequentially from the cutting edge to a center thereof, thereby giving the relationship of θ2>θ1>θ3>0.
Further, Patent Document 2 proposes a cutting insert in which, for the purpose of treating chips in particular on high-feed rate medium cutting with low depth of cut, a first rake face inclined downward from a cutting edge and a second rake face inclined to a greater extent than the first rake face are continuously formed, a breaker is installed which rises on an upper face in the vicinity of a nose portion, an auxiliary protrusion having an angular shape is also installed from the first rake face in the vicinity of the nose portion to the breaker, and an inclination angle θ of a ridge line of the auxiliary protrusion, an inclination angle θ1 of the first rake face and an inclination angle θ2 of the second rake face 13 satisfy a relationship of θ1<θ<θ2.